A wide variety of commercial silicone polymers are produced by the hydrolysis of a few basic chlorosilanes. These important chlorosilane monomers are produced by processes that also yield aqueous hydrochloric acid as a major by-product. For example, the hydrolysis of dimethyl-dichlorosilane yields 2 moles of hydrogen chloride for every mole of chlorosilane hydrolyzed. Because of the commercial importance of these and other processes for producing chlorosilanes, large amounts of by-product aqueous hydrochloric acid streams are generated.
Aqueous hydrochloric acid resulting as a by-product from the hydrolysis of chlorosilanes, as well as from other sources, is often contaminated with silicon containing materials, primarily silanols and siloxanes. Additionally other contaminants may be present such as solvents, hydrocarbons, and chlorinated hydrocarbons. Removal of these materials has proven a problem, particularly when relatively small concentrations of these materials are objectionable.
The bulk of these materials may phase separate as an oil layer on the aqueous hydrochloric acid and thus can be separated utilizing various techniques, but there remains small concentrations, typically below about 1000 milligrams per liter (mg/l), of these materials which are still soluble or stable in the aqueous hydrochloric acid. Some of this by-product hydrochloric acid can be re-used for various commercial applications if it is cleaned up.
However, much of the aqueous hydrochloric acid ends up as waste streams that must be neutralized and disposed of because the level of undesirable contaminants prevents its use for many applications. This represents not only an economic loss of a valuable source of chloride ion for commercial production of chlorosilane intermediates but also poses a potential negative impact on the environment, by impacting the level of total dissolved solids present in commercial wastewater streams.
To the applicants knowledge, there does not seem to be any patents or other publications directed to the separation of soluble or stable silanols and siloxanes from aqueous hydrochloric acid. Such silanols and siloxanes are reactive and can undergo condensation polymerization when in contact with hydrochloric acid.
One object of this present invention is to provide a process by which aqueous hydrochloric acid can be more easily purified. Another object is to provide a process by which small concentrations of silicon containing impurities can be more easily removed from aqueous hydrochloric acid such that the hydrochloric acid is made suitable for re-use. Still another object of this invention is to economically refurbish aqueous hydrochloric acid streams to greatly reduce the chloride ion that must be neutralized and disposed of. These and other objects of this invention will become apparent to one of ordinary skill in the art after reading this specification.